How to Use Ventricular Assist Devices to Facilitate Ablation of Hemodynamically Unstable Ventricular Tachycardia

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How to Use Ventricular Assist Devices to Facilitate Ablation of Hemodynamically Unstable Ventricular Tachycardia


Chandrasekar Palaniswamy, MBBS, MD; Marc A. Miller, MD; Vivek Y. Reddy, MD; Srinivas R. Dukkipati, MD


Introduction


Catheter ablation for treatment of ventricular tachycardia (VT) may be performed using 2 different ablation strategies. Substrate-based mapping targets the putative channels for VT that can be identified during sinus rhythm. This is an effective strategy in patients with ischemic cardiomyopathy where complex fractionated electrograms, late potentials, and local abnormal ventricular activities can be targeted in sinus rhythm.1 However, in patients with nonischemic cardiomyopathy, there is a relative paucity of these targets, thereby rendering this strategy significantly less effective.2 The second strategy involves entrainment and activation mapping with identification and ablation of the critical isthmus for VT.3 This may be the preferred strategy when the potential VT circuits are adjacent to critical anatomical structures such as the coronary artery or phrenic nerve where an extensive substrate-based ablation may be suboptimal due to the potential for collateral damage (Figure 58.1). However, hemodynamic instability during episodes of VT often precludes detailed mapping. Even repetitive brief episodes of unstable VT may negatively affect end-organ perfusion and result in hemodynamic decompensation. Vasopressors or inotropes may be used, but the extent of hemodynamic support provided is usually inadequate. Prolonged use of these agents may also be cardiotoxic, with increased risk for multi-organ dysfunction, morbidity, and mortality. Use of temporary mechanical circulatory support devices is an attractive strategy for activation and entrainment mapping of hemodynamically unstable VT.


Patient Selection


The decision regarding the need for mechanical support should be based on the patient’s cardiac status, including heart failure functional class and systolic function, the cycle length of clinical and inducible VTs, hemodynamic status during VT, myocardial substrate for VT, prior catheter ablations and reasons for prior ablation failure (such as inadequate activation/entrainment mapping due to hemodynamic intolerance), and the depth of anesthesia. While hemodynamic support may be beneficial in both ischemic and nonischemic cardiomyopathy, the benefit may be greater in patients with nonischemic cardiomyopathy where substrate-based ablation is less effective. Patients with nondilated left ventricle (LV) or significant LV hypertrophy are less likely to benefit from percutaneous LV assist device (pLVAD) such as Impella (Abiomed, Danvers, MA). Furthermore, pLVADs should be avoided in patients with disproportionately severe right ventricular dysfunction or advanced pulmonary hypertension, as they may demonstrate worsening of their hemodynamic profile with pLVADs. Due to direct unloading of the LV, the Impella device is more efficient in reducing LV end-diastolic pressure and myocardial oxygen demand compared to the TandemHeart (CardiacAssist, Inc., Pittsburgh, PA) at comparable flow rates. Furthermore, Impella requires smaller arterial sheaths and obviates the need for additional venous access and transeptal puncture, which may potentially reduce complications and shorten implantation times. In our center, Impella is therefore the preferred device for hemodynamic support for VT ablation. In cases where retrograde aortic approach is used for LV mapping, TandemHeart is preferred.



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Figure 57.1 Patient with nonischemic cardiomyopathy and VT undergoing epicardial ablation. The epicardial bipolar voltage map (top middle) and coronary angiogram (top left and right) are shown in left anterior oblique views. The location of the left anterior descending artery (LAD) and a diagonal artery (Diag) are shown with the ablation catheter positioned over them (yellow circles on voltage map). The voltage map shows numerous areas of late potentials (black points), fractionated electrograms (white points) in close proximity to the coronary arteries and phrenic nerve (blue points). The isthmus site (red point) of the clinical VT was identified with entrainment (lower left) and resulted in quick termination of the VT (lower right). An Impella pLVAD (yellow arrow) was used in this case to allow mapping and ablation during VT to avoid unnecessary ablation of sites with risk of injury to the phrenic nerve or coronary arteries.


In our experience, patient factors associated with pLVAD benefit during VT ablation include: (1) presentation with electrical storm, (2) nonischemic cardiomyopathy, (3) LV ejection fraction (LVEF) ≤ 30%, (4) class ≥ III heart failure, and (5) prior failed ablation.


Percutaneous Hemodynamic Support Devices


Table 57.1 provides a comparison of commonly used percutaneous hemodynamic support devices for VT ablation.


Table 57.1Percutaneous hemodynamic support devices







































Device


Insertion Technique


Mechanism of Support


Augmentation of Cardiac Output


Intra-aortic Balloon Pump Counterpulsation


Percutaneous or surgical 7.5- to 8-Fr access


Counterpulsation (systolic unloading and diastolic augmentation)


A0.5 L/min


Impella 2.5


Percutaneous or surgical 13-Fr single arterial acces


Axial flow pump delivering blood from LV to aorta


2.5 L/min


Impella CP


Percutaneous or surgical 14-Fr single arterial access

 

3.3 L/min


Impella 5.0


Surgical (femoral or axillary artery cutdown) 21-Fr single arterial access

 

5 L/min


TandemHeart


Percutaneous or surgical 21-Fr inflow (venous) – transseptal 15- or 17-Fr outflow (arterial)


Centrifugal, continuous flow pump


3.5–4.0 L/min


Extracorporeal Membrane Oxygenation (VA-ECMO)


Percutaneous or surgical 17- to 22-Fr venous, 15-Fr arterial cannula


Centrifugal continuous flow pump with quadrox oxygenator


2.5–4 L/min


Intra-Aortic Balloon Pump Counterpulsation


The benefits of the intra-aortic balloon pump (IABP) are its relatively small arterial sheath size (7.5- to 8-Fr), ease of insertion, and familiarity to lab personnel. The balloon is positioned in the descending aorta, with the distal end of the balloon lying a few centimeters distal to the origin of left subclavian artery and the proximal end above the renal arteries. Decrease in afterload by balloon inflation in systole augments LV performance. Inflation of the balloon in diastole augments the diastolic pressure and improves coronary and peripheral blood flow. Though IABP is widely used for hemodynamic support in cardiogenic shock, this is not ideally suited for patients undergoing VT ablation as this requires a stable, regular, and nontachycardic rhythm. Furthermore, IABP augments cardiac output only by 0.5 L/min, which may not provide adequate support during VT ablation. Optimal functioning of the IABP is dependent on timing of balloon inflation and deflation to pressure- or ECG-based triggers. Synchronization trigger used for balloon inflation during VT ablation should be either a “peak of QRS” trigger on surface ECG or arterial pressure waveform trigger. At our centers, we rarely use IABP support due to the minimal amount of hemodynamic support provided during VT.


Impella


The Impella device comprises a miniaturized impeller-driven axial flow pump placed temporarily through the aortic valve to pump blood directly from the LV to the ascending aorta. Three Impella devices with different pump-flow capabilities are relevant for hemodynamic support during VT ablation: The Impella 2.5, placed through a 13-Fr introducer sheath in the femoral artery and delivering a maximal flow rate of 2.5 L/min; Impella CP, placed through a 14-Fr access sheath, allowing flow rate of approximately 3.5 L/min; and the Impella 5.0, which requires a surgical cutdown for arterial access (21-Fr sheath) but which is capable of providing a maximal support of about 5.0 L/min. Of these, most clinical experience thus far with VT ablation has been with the Impella 2.5 device, though the widely available 3.5 device is increasingly being adopted for use during VT ablation procedures.


The pLVAD implant technique for patients undergoing VT ablation is as follows.4 Percutaneous vascular access is obtained in the (usually left) common femoral artery with care to ensure that the puncture is above the level of femoral artery bifurcation. Contrast is administered to ensure the level of access and to rule out significant peripheral arterial disease. The arteriotomy tract is then dilated with a 6- to 8.5-Fr sheath. Prior to upsizing to the 13-Fr or 14-Fr sheath, “preclosure” of the arteriotomy is performed using 2 orthogonally placed 6-Fr Perclose vascular closure devices (Abbott Vascular, Redwood City, CA). “Preclosure” helps with rapid hemostasis after removal of the arterial sheath at the end of the procedure. After upsizing the sheath to the final large-bore introducer needed to accommodate the pLVAD system, anticoagulation with intravenous heparin is initiated to achieve target ACT of greater than 250 seconds (Figure 57.2). The pLVAD is advanced retrograde through the aorta over a 0.018-inch guidewire (inserted through JR4, AL-1, multipurpose or pigtail catheters), and across the aortic valve such that the inlet of the device is positioned in the LV approximately 4 cm below the aortic valve annulus, with the outlet in the aortic root. Figure 57.3 is an example of an attempt to insert the Impella CP across the aortic valve without the use of a guidewire, followed by successful implantation with the over-the-wire technique (image Video 57.1). After confirming the appropriate positioning of the device with fluoroscopy and intracardiac echocardiography, the device is turned on and titrated up to its full support capability. Proper device positioning should then be reconfirmed using the positioning waveform on the console. As the device position may change during episodes of VT or after abrupt termination of tachycardia, the positioning of the device should be monitored throughout the procedure, and can typically be corrected with minor manipulation of the shaft at the level of the femoral access sheath.



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Figure 57.2 Common femoral artery access and “preclosure” for pLVAD implantation. Panel A: Left common femoral artery access is confirmed by performing an angiogram followed by placement of an 8-Fr sheath. The caliber of the femoral and iliac arteries is also assessed for suitability of the pLVAD. Panel B: “Preclosure” is performed by placing 2 orthogonally placed Perclose devices, which are secured to the field using clamps (arrows). The 8-Fr sheath is then upsized to a 14-Fr sheath and the Impella CP can be placed as seen.

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Aug 27, 2018 | Posted by in CARDIOLOGY | Comments Off on How to Use Ventricular Assist Devices to Facilitate Ablation of Hemodynamically Unstable Ventricular Tachycardia
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